2 30 POPULAR SCIENCE MONTHLY. 



for twelve days or longer." In the third ease, that of Dr. Lazear, the 

 facts are stated in the report of the board as follows : 



Case 3. Dr. Jesse W. Lazear, Acting Assistant Surgeon U. S. Army, a mem- 

 ber of this board, was bitten on August 16, 1900 (Case 3, Table III) by a mos- 

 quito (Culex fasciatus) which ten days previously had been contaminated by 

 biting a very mild case of yellow fever (fifth day). No appreciable disturbance 

 of health followed this inoculation. 



On September 13, 1900 (forenoon). Dr. Lazear, while on a visit to Las 

 Animas Hospital, and while collecting blood from yellow fever patients for 

 study, was bitten by a Culex mosquito (variety undetermined). As Dr. Lazear 

 had been previously bitten by a contaminated insect without after effects, he 

 deliberately allowed this particular mosquito, which had settled on the back 

 of his hand, to remain until it had satisfied its hunger. 



On the evening of September 18, 5 days after the bite. Dr. Lazear com- 

 plained of feeling 'out of sorts,' and had a chill at 8 p. m. 



On September 19, 12 o'clock noon, his temperature was 102.4°, pulse 112; 

 his eyes were injected and his face suffused; at 3 p. m. temperature was 103.4°, 

 pulse 104; 6 p. m., temperature 103.8° and pulse 106; albumin appeared in the 

 urine. Jaundice appeared on the third day. The subsequent history of this case 

 was one of progressive and fatal yellow fever, the death of our much-lamented 

 colleague having occurred on the evening of September 25, 1900. 



Evidently in this case the evidence is not satisfactory as to the fatal 

 attack being a result of the bite by a mosquito 'while on a visit to Las 

 Animas Hospital/ although Dr. Lazear himself was thoroughly con- 

 vinced that this was the direct cause of his attack. 



The inference drawn by Dr. Eeed and his associates, from the ex- 

 periments thus far made, was that yellow fever may be transmitted by 

 mosquitoes of the genus Culex, but that in order to convey the infection 

 to a non-immune individual the insect must be kept for 12 days or 

 longer after it has filled itself with blood from a j^ellow fever patient in 

 the earlier stages of the disease. In other words, that a certain period 

 of incubation is required in the body of the insect before the germ 

 reaches its salivary glands and consequently before it is able to inoculate 

 an individual with the germs of yellow fever. This inference, based 

 upon experimental data, received support from other observations, 

 which have been repeatedly made, with reference to the introduction and 

 spread of yellow fever in localities favorable to its propagation. When 

 a case is imported to one of our southern seaport cities, from Havana, 

 Vera Cruz or some other endemic focus of the disease, an interval of 

 two weeks or more occurs before secondary cases are developed as a re- 

 sult of such importation. In the light of our present knowledge this is 

 readily understood. A certain number of mosquitoes having filled 

 themselves with blood from this first case after an interval of twelve days 

 or more bite non-immune individuals living in the vicinity, and these 

 individuals after a brief period of incubation fall sick with the disease ; 

 being bitten by other mosquitoes they serve to transmit the disease 



